Power control apparatus for a battery-powered communication system

ABSTRACT

A power control apparatus includes a first driven circuit and a second driven circuit connected to the first driven circuit. A primary power-supply circuit produces a primary voltage from a source voltage of a battery and supplies the primary voltage to drive the first driven circuit. A secondary power-supply circuit produces a secondary voltage from the source voltage of the battery or from the primary voltage of the primary power-supply circuit, and supplies the secondary voltage to drive the second driven circuit. A control circuit outputs a power-supply control signal to the secondary power-supply circuit in response to a command signal, so that the supply of the secondary voltage to the second driven circuit by the secondary power-supply circuit is started or terminated by the power-supply control signal.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a power control apparatus which issuitable for use in a battery-powered system, such as a cellular mobiletelephone or a portable electronic device.

(2) Description of the Related Art

A power control apparatus provided in a battery-powered system, such asa cellular mobile telephone or a portable electronic device, is known.In the power control apparatus, a source voltage of a battery isconverted into a controlled voltage, and the controlled voltage issupplied to each of driven circuits (or functional elements) of thesystem. There is a demand for the power control apparatus of this typeto reduce a power consumption of the driven circuits. In recent years,the power control apparatus of this type has been improved for thepurpose of reducing a power consumption of the driven circuits.

For example, Japanese Laid-Open Patent Application No. 5-088790discloses a power control system which is adapted to allow a sleep-modeoperation of a CPU (central processing unit) in which the operation ofthe CPU is assured and the power of the CPU is turned OFF.

Japanese Laid-Open Patent Application No. 5-265597 discloses amicro-controller which allows a driven circuit to operate at a lowvoltage in a selected mode. In the micro-controller, a source voltagesupplied to the driven circuit is controlled so as to meet one of powerconsumption reduction, operating speed increase and noise reductionmodes.

Japanese Laid-Open Patent Application No. 6-139373 discloses asemiconductor device provided with a switch selectable between a normalpower mode and a power saving mode. In the semiconductor device, avoltage supplied to a driven circuit is controlled by setting the switchto select one of the two modes.

FIG. 7 shows a conventional power control apparatus. The conventionalpower control apparatus of FIG. 7 includes a power-supply circuit 61which supplies a source voltage of a first battery 60a through a diode80 to a driven circuit 71. A power-supply circuit 62 supplies the sourcevoltage of the first battery 60a to each of a driven circuit 72 and apower-supply circuit 63. The power-supply circuit 63 supplies a lowervoltage, derived from the source voltage of the first battery 60a orfrom the power-supply circuit 62, to a driven circuit 73. A sourcevoltage of a second battery 60b is supplied through a diode 81 to thedriven circuit 71.

In the conventional power control apparatus of FIG. 7, the secondbattery 60b and the diode 81 constitute a backup power supply that actsto supply the source voltage of the second battery 60b to the drivencircuit 71 when the source voltage of the first battery 60a supplied tothe driven circuit 71 by the power-supply circuit 61 is discontinued.The power-supply circuit 63 acts as a dependent circuit that operates independence on a power-supply operation of the power-supply circuit 62.That is, the dependent power-supply circuit 63 operates to supply thelower voltage to the driven circuit 73 when the power-supply circuit 62is operating. The dependent power-supply circuit 63 may include a DC-DCconverter or a voltage regulator.

The relationship between the power-supply circuit 62 and the dependentpower-supply circuit 63 is needed when the conventional power controlapparatus includes functional blocks indicated by a dotted line in FIG.7. That is, the relationship between the power-supply circuit 62 and thedependent power-supply circuit 63 is needed when one of the functionalblocks (for example, the driven circuit 72) is driven by thepower-supply circuit 72 at the source voltage of the battery 60a whilethe other functional block (for example, the driven circuit 73) isdriven by the power-supply circuit 63 at the lower voltage derived fromthe source voltage.

In the conventional power control apparatus of FIG. 7, each of thedriven circuits 71, 72 and 73 is provided with an oscillation circuit.When the oscillation circuit generates a clock signal with a loweredfrequency and supplies the clock signal to the driven circuit ofconcern, the driven circuit is set in a low-speed mode so that itoperates at a low speed. When the oscillation circuit stops supplyingthe clock signal, the driven circuit of concern is set in a stand-bymode. By using the oscillation circuits of the driven circuits 71, 72and 73, the conventional power control apparatus of FIG. 7 acts toreduce the power consumption of the driven circuits 71, 72 and 73.

In the convectional power control apparatus of FIG. 7, if the sourcevoltage is continuously supplied to the driven circuit of concern duringthe stand-by mode, it is difficult to completely prevent the flow of aleak current from a MOS (metal oxide semiconductor) transistor of thedriven circuit. In order to eliminate this problem, it is necessary forthe power-supply circuits 61 and 62 to stop the supplying of the sourcevoltage of the first battery 60a to the driven circuits 71 and 72 whenthe driven circuit is in the stand-by mode.

However, in the conventional power control apparatus of FIG. 7, thepower-supply circuit 63 continues to supply the lower voltage to thedriven circuit 73 during the operation of the power-supply circuit 62.Even when the operation of the driven circuit 73 is not needed, thepower-supply circuit 63 continuously supplies the lower voltage to thedriven circuit 73. In such a condition, the driven circuit 73unnecessarily consumes the power supplied by the power-supply circuit63, and the conventional power control apparatus of FIG. 7 does not actto reduce the power consumption of the driven circuit 73.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved powercontrol apparatus in which the above-described problems are eliminated.

Another object of the present invention is to provide a power controlapparatus which is effective in reducing a power consumption of a drivencircuit by suitably controlling a power-supply operation of a secondarypower-supply circuit which supplies power to the driven circuit independence on a power-supply operation of a primary power-supplycircuit.

The above-mentioned objects of the present invention are achieved by apower control apparatus including: a first driven circuit; a seconddriven circuit which is connected to the first driven circuit; a primarypower-supply circuit which produces a primary voltage from a sourcevoltage of a battery and supplies the primary voltage to drive the firstdriven circuit; a secondary power-supply circuit which produces asecondary voltage from the source voltage of the battery or from theprimary voltage of the primary power-supply circuit and supplies thesecondary voltage to drive the second driven circuit; and a controlcircuit which outputs a power-supply control signal to the secondarypower-supply circuit in response to a command signal, so that the supplyof the secondary voltage to the second driven circuit by the secondarypower-supply circuit is started or terminated by the power-supplycontrol signal.

The above-mentioned objects of the present invention are achieved by apower control apparatus including: a first driven circuit; a seconddriven circuit which is connected to the first driven circuit; a primarypower-supply circuit which is connected to a battery, the primarypower-supply circuit producing a primary voltage from a source voltageof the battery and supplying the primary voltage to drive the firstdriven circuit; a secondary power-supply circuit which is connected tothe primary power-supply circuit, the secondary power-supply circuitproducing a secondary voltage from the source voltage of the battery orfrom the primary voltage of the primary power-supply circuit andsupplying the secondary voltage to drive the second driven circuit; aprimary oscillation part which outputs a clock signal to the firstdriven circuit; a primary reset generating part which outputs a primaryreset signal to the first driven circuit when an oscillation of theprimary oscillation part is detected to be stable, the primary resetsignal causing the first driven circuit to start operation in accordancewith the clock signal output by the primary oscillation part; a controlsignal generating part, connected to both the first driven circuit andthe secondary power-supply circuit, which outputs a power-supply controlsignal to the secondary power-supply circuit in response to a commandsignal output by the first driven circuit, so that the supply of thesecondary voltage to the second driven circuit by the secondarypower-supply circuit is started or terminated by the power-supplycontrol signal; a secondary oscillation part which outputs a clocksignal to the second driven circuit; and a secondary reset generatingpart which outputs a secondary reset signal to the second driven circuitwhen an oscillation of the secondary oscillation part is detected to bestable, the secondary reset signal causing the second driven circuit tostart operation in accordance with the clock signal output by thesecondary oscillation part.

The power control apparatus according to the present invention iseffective in reducing the power consumption of the second driven circuitin contrast to the conventional power control apparatus. In a preferredembodiment of the power control apparatus of the present invention, thepower-supply operation of the secondary power-supply circuit is suitablycontrolled such that the supply of the secondary voltage to the seconddriven circuit is enabled by a high-state power-supply control signalonly when it is needed, and the supply of the secondary voltage to thesecond driven circuit is disabled by a low-state power-supply controlsignal when it is unneeded. In a preferred embodiment of the powercontrol apparatus of the present invention, the oscillation of thesecondary oscillation part is quickly stabilized after a start commandsignal is output to the control signal generating part by the firstdriven circuit, and it is possible to achieve a speedy power-supplyoperation of the first and second driven circuits. Further, a preferredembodiment of the power control apparatus of the present invention actsto prevent the flow of a leak current from the first driven circuit intothe second driven circuit when the supply of the secondary voltage tothe second driven circuit is stopped, and it is possible to moreeffectively reduce the power consumption of the driven circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of a power control apparatus embodying thepresent invention;

FIG. 2 is a circuit diagram of a control circuit of the power controlapparatus of FIG. 1;

FIG. 3 is a time chart for explaining operations of the control circuitof the power control apparatus of FIG. 2;

FIG. 4 is a time chart for explaining power-saved periods during anoperation of the power control apparatus of FIG. 1;

FIG. 5 is a circuit diagram of a modification of a secondary oscillationcircuit in the control circuit of FIG. 2;

FIG. 6A and FIG. 6B are circuit diagrams of a modification of first andsecond driven circuits in the power control apparatus of FIG. 1; and

FIG. 7 is a block diagram of a conventional power control apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given of the preferred embodiments of thepresent invention with reference to the accompanying drawings.

FIG. 1 shows an embodiment of a power control apparatus of the presentinvention.

As shown in FIG. 1, the power control apparatus in the presentembodiment includes a power-supply circuit 2 which supplies a sourcevoltage of a battery 10 through a diode 4 to a driven circuit 5. Asource voltage of a battery 1 is supplied through a diode 3 to thedriven circuit 5. The battery 1 and the diode 3 constitute a backuppower supply that acts to supply the source voltage of the battery 1 tothe driven circuit 5 when the source voltage of the battery 10 suppliedto the driven circuit 5 by the power-supply circuit 2 is discontinued.

The elements 1, 2, 3, 4 and 5 of the power control apparatus, shown inFIG. 1, are essentially the same as the elements 60a, 61, 81, 80 and 71of the conventional power control apparatus of FIG. 7, respectively, anda description thereof will be omitted for the sake of simplicity ofdescription.

In the power control apparatus of FIG. 1, a primary power-supply circuit11 has an input connected to the battery 10. The battery 10 is, forexample, a 5-V battery. A secondary power-supply circuit 12 has an inputconnected to an output of the primary power-supply circuit 11. Theprimary power-supply circuit 11 produces a primary voltage (for example,3 V) from the source voltage of the battery 10, and supplies the primaryvoltage through a power-supply line 31 to a first driven circuit 21. Thesecondary power-supply circuit 12 produces a secondary voltage (forexample, 2 V) from the source voltage of the battery 10 or from theprimary voltage of the primary power-supply circuit 11, and supplies thesecondary voltage through a power-supply line 32 to a second drivencircuit 22.

The secondary power-supply circuit 12 acts as a dependent circuit thatoperates in dependence on a power-supply operation of the primarypower-supply circuit 11. That is, the dependent power-supply circuit 12operates to supply the secondary voltage to the second driven circuit 22when the first power-supply circuit 11 is operating.

The first driven circuit 21 and the second driven circuit 12 areinterconnected by a dial line 23. A data signal output by the firstdriven circuit 21 is received by the second driven circuit 22 throughthe data line 23, and the second driven circuit 22 processes thereceived data. A data signal, indicating the processed data, output bythe second driven circuit 22 is received by the first driven circuit 21,and the first driven circuit 21 further processes the received data.

The first driven circuit 21 and the second driven circuit 22 do notnecessarily start operation at the same time. The first driven circuit21 may solely start operation when the second driven circuit 22 stopsoperation. The second driven circuit 22 may not solely start operationwhen the first driven circuit 21 stops operation. The second drivencircuit 22 starts operation only when the first driven circuit 21 isoperating.

In the power control apparatus of FIG. 1, a control circuit 13 whichincludes a voltage detection unit 130 and a secondary power control unit131 is provided.

FIG. 2 shows a configuration of the control circuit 13 of the powercontrol apparatus of FIG. 1. FIG. 3 is a time chart for explainingoperations of the control circuit of FIG. 2. The control circuit 13,including the voltage detection unit 130 and the secondary power controlunit 131, is indicated by a dotted line in FIG. 2.

A description will be given of the configuration and operations of thecontrol circuit of the power control apparatus in the present embodimentwith reference to FIG. 2 and FIG. 3.

As indicated by (a) in FIG. 3, after a delay of a given period from astart of operation of the primary power-supply circuit 11, the primarypower-supply circuit 11 is set in an operating condition that it cansupply the primary voltage (for example, 3 V) to the first drivencircuit 21.

The voltage detection unit 130 includes a primary voltage detection part130a and a secondary voltage detection part 130b as shown in FIG. 2. Asindicated by (b) in FIG. 3, the primary voltage detection part 130adetects the primary voltage supplied by the primary power-supply circuit11 when the primary power-supply circuit 11 is set in the operatingcodition, and outputs a high-state signal to the secondary power controlunit 131 of the control circuit 13.

The secondary power control unit 131 includes a primary oscillation part133 as shown in FIG. 2. As indicated by (c) in FIG. 3, the primaryoscillation part 133 starts oscillation at the same time as the start ofoperation of the primary power-supply circuit 11. After a delay of agiven period, a clock signal (CK) produced by the oscillation of theprimary oscillation part 133 becomes stable.

The secondary power control unit 131 includes a primary reset generatingpart 132, and the primary reset generating part 132 is constructed bytwo flip-flop circuits which are connected in a manner shown in FIG. 2.As indicated by (d) in FIG. 3, after a delay of a given period since thetime the high-state signal is output by the primary voltage detectionpart 130a, the primary reset generating part 132 outputs a high-statesignal (or a primary reset signal) to the first driven circuit 21.

When the primary reset signal output by the primary reset generatingpart 132 is received, the first driven circuit 21 starts operation. Atthe start of operation, the stable clock signal (CK) output by theprimary oscillation part 133 is supplied to the first driven circuit 21,and the primary voltage output by the primary power-supply circuit 11 issupplied to the first driven circuit 21 through the power-supply line31. The primary oscillation part 133 and the primary reset generatingpart 132 are driven by the power supplied from the primary power-supplycircuit 11.

The secondary power control unit 131 includes a control signalgenerating part 136 as shown in FIG. 2. When transmitting the processeddata from the first driven circuit 21 to the second driven circuit 22via the data line 23, the first driven circuit 21 sends a start commandsignal to the control signal generating part 136. The start commandsignal causes the control signal generating part 136 to output apower-supply control signal (or a high-state signal) to the secondarypower-supply circuit 12. As the secondary power-supply circuit 12 startssupplying the secondary voltage to the second driven circuit 12 inresponse to the high-state power-supply control signal, the seconddriven circuit 22 quickly starts operation by the power supplied fromthe secondary power-supply circuit 12.

As indicated by (e) in FIG. 3, when the start command signal output bythe first driven circuit 21 is received, the control signal generatingpart 136 outputs the power-supply control signal (or the high-statesignal) to each of the secondary power-supply circuit 12 and thesecondary voltage detection part 130b.

On the other hand, when receiving the processed data from the seconddriven circuit 22 at the first driven circuit 21 via the data line 23,the first driven circuit 21 sends an end command signal to the controlsignal generating part 136. The end command signal causes the controlsignal generating part 136 to output a low-state power-supply controlsignal to the secondary power-supply circuit 12. As the secondarypower-supply circuit 12 stops supplying the secondary voltage to thesecond driven circuit 22 in response to the low-state power-supplycontrol signal, the second driven circuit 22 quickly terminates thepower-supply operation after the processed data from the second drivencircuit 22 is supplied to the first driven circuit 21.

As indicated by (e) in FIG. 3, when the end command signal output by thefirst driven circuit 21 is received, the control signal generating part136 outputs the low-state power-supply control signal to each of thesecondary power-supply circuit 12 and the secondary voltage detectionpart 130b.

In the control circuit 13 of FIG. 2, the detection signal output by theprimary voltage detection part 130a is supplied through a signal line 24to the control signal generating part 136. Even when the start commandsignal output by the first driven circuit 21 is received, the controlsignal generating part 136 acts to delay the start of operation of thesecondary power-supply circuit 12 until a high-state detection signaloutput by the primary voltage detection part 130a is received. When alow-state detection signal output by the primary voltage detection part130a is received, the control signal generating part 136 acts to stopthe operation of the secondary power-supply circuit 12.

The secondary voltage detection part 130b starts operation when thehigh-state power-supply control signal output by the control signalgenerating part 136 is received. Also, the secondary power-supplycircuit 12 starts operation when the high-state power-supply controlsignal is received. As indicated by (f) in FIG. 3, after a delay of agiven period from the start of operation, the secondary power-supplycircuit 12 is set in a operating condition that it can supply thesecondary voltage (for example, 2 V) to the second driven circuit 22.

The secondary power control unit 131 includes a secondary resetgenerating part 134 and a secondary oscillation part 135 as shown inFIG. 2. As indicated by (g) in FIG. 3, the secondary voltage detectionpart 130b detects the secondary voltage supplied by the secondarypower-supply circuit 12 when the secondary power-supply circuit 12 isset in the operating condition, and outputs a high-state signal to eachof the secondary reset generating part 134 and the secondary oscillatorpart 135 of the secondary power control unit 131.

As indicated by (h) in FIG. 3, the secondary oscillation part 135 startsoscillation at the same time as the start of operation of the secondarypower-supply circuit 12. After a delay of a given period, a clock signal(CK) produced by the oscillation of the secondary oscillation part 135becomes stable.

The secondary reset generating part 134 of the secondary power controlunit 131 is constructed by two flip-flop circuits which are connected ina manner shown in FIG. 2. As indicated by (i) in FIG. 3, after a delayof a given period since the time the high-state signal is output by thesecondary voltage detection part 130b, the secondary reset generatingpart 134 outputs a high-stage signal (or a secondary reset signal) tothe second driven circuit 22.

When the secondary reset signal output by the secondary reset generatingpart 134 is received, the second driven circuit 22 starts operation. Atthe start of operation, the stable clock signal (CK) output by thesecondary oscillation part 135 is supplied to the second driven circuit22, and the secondary voltage output by the secondary power-supplycircuit 12 is supplied to the second driven circuit 22 through thepower-supply line 32. The secondary oscillation part 135 and thesecondary reset generating part 134 are driven by the power suppliedfrom the secondary power-supply circuit 12.

As previously described, in the conventional power control apparatus ofFIG. 7, even when the operation of the driven circuit 73 is not needed,the power-supply circuit 63 continuously supplies the lower voltage tothe driven circuit 73. In such a condition, the driven circuit 73unnecessarily consumes the power supplied by the power-supply circuit63.

FIG. 4 shows power-saved periods during an operation of the powercontrol apparatus of FIG. 1.

In contrast to the conventional power control apparatus of FIG. 7, theabove-described embodiment of the power control apparatus is effectivein reducing the power consumption of the second driven circuit 22. Asshown in FIG. 4, the power-supply operation of the secondarypower-supply circuit 12 is suitably controlled such that the supply ofthe secondary voltage to the second driven circuit 22 is enabled by thehigh-state power-supply control signal only when it is needed, and thesupply of the secondary voltage to the second driven circuit 22 isdisabled by the low-state power-supply control signal when it isunneeded.

In order to achieve a speedy power-supply operation of the first andsecond driven circuits 21 and 22, it is necessary that the oscillationof the secondary oscillation part 135 becomes stable as quickly aspossible after the start command signal is output to the control signalgenerating part 136 by the first driven circuit 21.

FIG. 5 shows a modification of the secondary oscillation part 135 in thecontrol circuit of FIG. 2. A secondary oscillation circuit 135′ shown inFIG. 5 is provided in order to achieve a speedy power-supply operationof the first and second driven circuits 21 and 22. In FIG. 5, theelements which are essentially the same as corresponding elements inFIG. 2 are designated by the same reference numerals, and a descriptionthereof will be omitted.

The secondary oscillation circuit 135′ of FIG. 5 is constructed by atwo-input AND gate and a PLL (phase-locked loop) circuit which areconnected in a manner shown in FIG. 5. The AND gate has an inputconnected to an output of the control signal generating part 136, and aninput connected to an output of the primary oscillation part 133. TheAND gate has an output connected to an input of the PLL circuit. The PLLcircuit has another input connected to an output of the secondaryvoltage detection part 130b. In response to a high-state clock signaloutput by the AND gate, the PLL circuit quickly produces a stable clocksignal with a locked frequency, and supplies it to the second drivencircuit 22.

In the secondary oscillation circuit 135′ of FIG. 5, when thepower-supply control signal at the output of the control signalgenerating part 136 is held in a high state, the AND gate passing theclock signal, supplied by the primary oscillation part 133, to the PLLcircuit. When a high-state clock signal output by the AND gate isreceived, the PLL circuit quickly produces a stable clock signal withthe locked frequency, and supplies it to the second driven circuit 22.Hence, it is possible to achieve a speedy power-supply operation of thefirst and second driven circuits 21 and 22.

Further, in order to more effectively reduce the power consumption ofthe driven circuits, it is desirable to prevent the flow of a leakcurrent from the first driven circuit 21 into the second driven circuit22 when the supply of the secondary voltage to the second driven circuit22 is stopped. When there is a difference in a drive voltage between thefirst driven circuit 21 and the second driven circuit 22, it isnecessary to eliminate the voltage difference.

FIG. 6A and FIG. 6B show a modification of the first and second drivencircuits 21 and 22 in the power control apparatus of FIG. 1.

In FIG. 6A, the first driven circuit 21 has inputs at which two-inputAND gates 21a are provided, and the second driven circuit 22 has inputsat which buffer gates 22a are provided. Data signals output by thesecond drive circuit 22 are supplied to the AND gates 21a at the inputsof the first driven circuit 21, and data signals output by the firstdriven circuit 21 are supplied to the buffer gates 22a at the inputs ofthe second driven circuit 22. In FIG. 6B, an example of theconfiguration of the respective inputs of the first and second drivencircuits 21 and 22 is shown, in which one of the two-input AND gates 21aand one of the buffer gates 22a, shown in FIG. 6A, are constructed byMOS transistors and resistors which are connected in series as shown inFIG. 6B.

The first and second driven circuits 21 and 22 shown in FIG. 6A and FIG.6B are provided to prevent the flow of a leak current from the firstdriven circuit 21 in the second driven circuit 22 when the supply of thesecondary voltage to the second driven circuit 22 is stopped.

As shown in FIG. 6A, at the inputs of the first driven circuit 21, thetwo-input AND gates 21a are provided. Each AND gate 21a is constructedby a resistor and two MOS transistors. The resistor and the two MOStransistors are connected in series between a primary voltage line and agrounded base in a manner shown in FIG. 6B. Each AND gate 21a has aninput (or a gate of one of the MOS transistors) connected to a signalline from the second driven circuit 22, and has an input (or a gate ofthe other MOS transistor) connected to an output (the power-supplycontrol signal) of the control signal generating part 136.

When the power-supply control signal at the output of the control signalgenerating part 136 is held in a high state, the AND gate 21a sets thefirst driven circuit 21 in an operating condition that it can receive adata signal supplied by the second driven circuit 22 via the signalline. When the data signal that is set in a high state by the seconddriven circuit 22 is received, the AND gate 21a of the first drivencircuit 21 converts the received data into a high-state data signalbased on the primary voltage.

As shown in FIG. 6A, at the inputs of the second driven circuit 22, thebuffer gates 22a are provided. Each buffer gate 22a is constructed by aresistor and a MOS transistor. The resistor and the MOS transistor areconnected in series between a secondary voltage line and a grounded basein a manner shown in FIG. 6B. Each buffer gate 22a has an input (or agate of the MOS transistor) connected to a signal line from the firstdriven circuit 21, and has an output connected to an internal element(not shown) of the second driven circuit 22. When the data signal thatis set in a high state by the first driven circuit 21 is received fromthe signal line, the buffer gate 22a of the second driven circuit 22converts the received data into a high-state data signal based on thesecondary voltage.

In the above-described embodiment of the power control apparatus inwhich the first and second driven circuits 21 and 22 of FIG. 6A and FIG.6B are provided, it is possible to prevent the flow of a leak currentfrom the MOS transistor of the first driven circuit 21 into the seconddriven circuit 22 when the supply of the secondary voltage to the seconddriven circuit 22 is stopped. Hence, it is possible to more effectivelyreduce the power consumption of the first and second driven circuits 21and 22.

Further, the present invention is not limited to the above-describedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

The present invention is based on Japanese priority application No.10-067305, filed on Mar. 17, 1998, the entire contents of which arehereby incorporated by reference.

1. A power control apparatus comprising: a first driven circuit; asecond driven circuit connected to the first driven circuit; a primarypower-supply circuit for producing a primary voltage from a sourcevoltage of a battery and supplying the primary voltage to drive thefirst driven circuit; a secondary power-supply circuit for producing asecondary voltage from the source voltage of the battery or from theprimary voltage of the primary power-supply circuit, and for supplyingthe secondary voltage to drive the second driven circuit; and controlmeans for outputting a power-supply control signal to the secondarypower-supply circuit in response to a command signal from the firstdriven circuit, so that the supply of the secondary voltage to thesecond driven circuit by the secondary power-supply circuit is startedor terminated by the power-supply control signal.
 2. The apparatusaccording to claim 1, wherein the control means outputs a high-statepower-supply control signal to the secondary power-supply circuit inresponse to a start command signal output by the first driven circuit,the high-state power-supply control signal causing the secondarypower-supply circuit to start the supply of the secondary voltage to thesecond driven circuit.
 3. The apparatus according to claim 1, whereinthe control means outputs a low-state power-supply control signal to thesecondary power-supply circuit in response to an end command signaloutput by the first driven circuit, the low-state power-supply controlsignal causing the secondary power-supply circuit to terminate thesupply of the secondary voltage to the second driven circuit.
 4. A powercontrol apparatus comprising: a first driven circuit; a second drivencircuit connected to the first driven circuit; a primary power-supplycircuit connected to a battery, the primary power-supply circuitproducing a primary voltage from a source voltage of the battery andsupplying the primary voltage to drive the first driven circuit; asecondary power-supply circuit connected to the primary power-supplycircuit, the secondary power-supply circuit producing a secondaryvoltage from the source voltage of the battery or from the primaryvoltage of the primary power-supply circuit and supplying the secondaryvoltage to drive the second driven circuit; a primary oscillation partfor outputting a clock signal to the first driven circuit; a primaryreset generating part for outputting a primary reset signal to the firstdriven circuit when an oscillation of the primary oscillation part isdetected to be stable, the primary reset signal causing the first drivencircuit to start operation in accordance with the clock signal output bythe primary oscillation part; a control signal generating part,connected to both the first driven circuit and the secondarypower-supply circuit, for outputting a power-supply control signal tothe secondary power-supply circuit in response to a command signaloutput by the first driven circuit, so that the supply of the secondaryvoltage to the second driven circuit by the secondary power-supplycircuit is started or terminated by the power-supply control signal; asecondary oscillation part for outputting a clock signal to the seconddriven circuit; and a secondary reset generating part for outputting asecondary reset signal to the second driven circuit when an oscillationof the secondary oscillation part is detected to be stable, thesecondary reset signal causing the second driven circuit to startoperation in accordance with the clock signal output by the secondaryoscillation part.
 5. The apparatus according to claim 4, wherein thesecondary oscillation part includes a gate circuit and a phase-lockedloop PLL circuit, the gate circuit having a first input connected to anoutput of the control signal generating part, a second input connectedto an output of the primary oscillation part, and an output connected toan input of the PLL circuit, the gate circuit passing the clock signalfrom the primary oscillation part to the PLL circuit when a high-statepower-supply control signal is received at the first input, the PLLcircuit producing a clock signal with a locked frequency when ahigh-state clock signal output by the gate circuit is received, andsupplying the clock signal to the second driven circuit.
 6. Theapparatus according to claim 4, wherein the second driven circuitincludes a buffer gate and an input of the second driven circuit, theinput of the second driven circuit being connected to an output of thefirst driven circuit via a signal line, the buffer gate, when a datasignal set in a high state by the first driven circuit is received fromthe signal line, converting the received data into a high-state datasignal based on the secondary voltage.
 7. The apparatus according toclaim 6, wherein the buffer gate includes a resistor and ametal-oxide-semiconductor transistor connected in series between asecondary voltage line and a grounded base.
 8. The apparatus accordingto claim 4, wherein the first driven circuit includes a gate circuit atan input of the first driven circuit, the input of the first drivencircuit being connected to an output of the second driven circuit via asignal line, the gate circuit having a first input connected to thesignal line and a second input connected to an output of the controlsignal generating part, the gate circuit enabling the first drivencircuit to receive a data signal from the signal line when a high-statepower-supply control signal output by the control signal generating partis received at the second input, and when the data signal that is set ina high state by the second driven circuit is received, the gate circuitconverting the received data into a high-state data signal based on theprimary voltage.
 9. The apparatus according to claim 8, wherein the gatecircuit includes a resistor and two metal-oxide-semiconductortransistors connected in series between a primary voltage line and agrounded base.
 10. The apparatus according to claim 4, wherein thecontrol signal generating part outputs a high-state power-supply controlsignal to the secondary power-supply circuit in response to a startcommand signal output by the first driven circuit, the high-statepower-supply control signal causing the secondary power-supply circuitto start the supply of the secondary voltage to the second drivencircuit.
 11. The apparatus according to claim 4, wherein the controlsignal generating part outputs a low-state power-supply control signalto the secondary power-supply circuit in response to an end commandsignal output by the first driven circuit, the low-state power-supplycontrol signal causing the secondary power-supply circuit to terminatethe supply of the secondary voltage to the second driven circuit.
 12. Apower control apparatus which drives a first driven circuit and a seconddriven circuit connected to the first driven circuit, comprising: aprimary power-supply circuit for producing a primary voltage from asource voltage of a battery, and supplying the primary voltage to drivethe first driven circuit; a secondary power supply circuit for producinga secondary voltage from the source voltage of the battery or from theprimary voltage of the primary power-supply circuit, and supplying thesecondary voltage to drive the second driven circuit; and control meansfor outputting a power-supply control signal to the secondarypower-supply circuit in response to a command signal from the firstdriven circuit, so that the supply of the secondary voltage to thesecond driven circuit by the secondary power-supply circuit is startedor terminated by the power-supply control signal.
 13. A power controlapparatus which drives a first driven circuit and a second drivencircuit connected to the first driven circuit, comprising: a primarypower-supply circuit for producing a primary voltage from a sourcevoltage of a battery, and supplying the primary voltage to drive thefirst driven circuit; a secondary power-supply circuit for producing asecondary voltage from the source voltage of the battery or from theprimary voltage of the primary power-supply circuit, and supplying thesecondary voltage to drive the second driven circuit; and a control unitoutputting a power-supply control signal to the secondary power-supplycircuit in response to a command signal from the first driven circuit,so that the supply of the secondary voltage to the second driven circuitby the secondary power-supply circuit is started or terminated by thepower control signal.
 14. A power control apparatus which drives a firstdriven circuit and a second driven circuit connected to the first drivencircuit, comprising: a primary power-supply circuit connected to abattery, the primary power-supply circuit producing a primary voltagefrom a source voltage of the battery, and supplying the primary voltageto drive the first driven circuit; a secondary power-supply circuitconnected to the primary power-supply circuit, the secondarypower-supply circuit producing a secondary voltage from the sourcevoltage of the battery or from the primary voltage of the primarypower-supply circuit, and supplying the secondary voltage to drive thesecond driven circuit; a pirmary oscillation unit outputting a clocksignal to the first driven circuit; a primary reset generating unitoutputting a primary reset signal to the first driven circuit when anoscillation of the primary oscillation unit is detected to be stable,the primary reset signal causing the first driven circuit to startoperation in accordance with the clock signal output by the primaryoscillation unit; a control signal generating unit connected to both thefirst driven circuit and the secondary power-supply circuit, the controlsignal generating unit outputting a power-supply control signal to thesecondary power-supply circuit in response to a command signal output bythe first driven circuit, so that the supply of the secondary voltage tothe second driven circuit by the secondary power-supply circuit isstarted or terminated by the power-supply control signal; a secondaryoscillation unit outputting a clock signal to the second driven circuit;and a secondary reset generating unit outputting a secondary resetsignal to the second driven circuit when an oscillation of the secondaryoscillation unit is detected to be stable, the secondary reset signalcausing the second driven circuit to start operation in accordance withthe clock signal output by the secondary oscillation unit.
 15. A powercontrol apparatus, comprising: a primary power-supply circuit forproducing a primary voltage from a source voltage of a battery, andtransmitting the primary voltage as a first driver signal; a secondarypower supply circuit for producing a secondary voltage from the sourcevoltage of the battery or from the primary voltage of the primarypower-supply circuit, and transmitting the secondary voltage as a seconddriver signal; voltage detecting and resetting means for generating adriver reset signal when the primary power supply circuit produces theprimary voltage; and control means for outputting a power-supply controlsignal to the secondary power-supply circuit in response to a commandsignal, so that the second driver signal is started or terminated by thepower-supply control signal.
 16. A power control apparatus, comprising:a primary power-supply circuit producing a primary voltage from a sourcevoltage of a battery, and transmitting the primary voltage as a firstdriver signal; a secondary power-supply circuit producing a secondaryvoltage from the source voltage of the battery or from the primaryvoltage of the primary power-supply circuit, and transmitting thesecondary voltage as a second driver signal; a voltage detection andresetting circuit for generating a driver reset signal when the primarypower supply circuit produces the primary voltage; and a control unitoutputting a power-supply control signal to the secondary power-supplycircuit in response to a command signal, so that the supply of thesecond driver signal is started or terminated by the power controlsignal.